The present invention relates to a valve spring used in a valve operating mechanism of an internal combustion engine for a vehicle such as an automobile.
As illustrated in FIG. 3, to decrease inertia mass of the valve operating mechanism, a coil valve spring 1 used in a valve operating mechanism of an internal combustion engine is formed like a frustum.
The upper and lower surfaces of the valve spring 1 are flat to contact the lower surface of a retainer 2 and the upper surface of a cylinder head 3 respectively, as shown in FIG. 3. In the frusto-conical valve spring 1, a diameter of an uppermost winding is smaller, so that a horizontal distance with a tubular portion of the retainer 2 becomes smaller. Thus, as illustrated in FIG. 3, the valve spring 1 vibrates in a lateral direction owing to surging, so that an inner circumferential edge 1a vigorously comes in contact with an inner corner 5 between the tubular portion 2a and a receiving surface 2b, thereby causing wear. As the inner corner 5 between the tubular portion 2a and the receiving surface 2b is subjected to large bending stress, wear thereon is unsuitable. The numerals 6, 7 and 8 denote a poppet valve, a valve guide and a pair of cotters respectively.